1. Field of the Invention
The present invention relates to a range switching apparatus of a shift-by-wire system for operating a shift range of an automatic transmission of a vehicle by using electric signals.
2. Description of the Related Art
Generally a vehicle is demanded to be stoppable and towable even if an abnormality occurs for any reason. In the case of a conventional vehicle, the vehicle can be stopped by switching the shift range of the automatic transmission to the P range or by using a parking brake. The vehicle can also be towed by switching the shift range of the automatic transmission from the P range to another range.
On the other hand, recently a shift-by-wire system, which switches the shift range of the automatic transmission of a vehicle by an electric signal based on an instruction of the vehicle driver, is used for vehicle control. In a vehicle to which the shift-by-wire system is applied, the shift range of the automatic transmission is electrically switched, hence if an abnormality occurs to the power supply or the power supply system, as in the case of a complete battery discharge, disconnection and the like, switching of the shift range of the automatic transmission becomes difficult. Therefore, even for a vehicle to which the shift-by-wire system is applied, a range switching apparatus, which allows switching the shift range of the automatic transmission even if an abnormality occurs for any reason, is demanded.
In the case of the conventional range switching apparatus, power to supply to a range control unit is stored in the capacitor. Therefore even if an abnormality occurs to the battery or power supply system, the automatic transmission can be switched to the P range at least once by using the power stored in the capacitor, whereby the vehicle can be stopped. The shift range of the automatic transmission can be manually switched from the P range to another range by operating a lever. Thereby the vehicle can be towed (e.g. see Japanese Patent No. 4833097).